340 NATURAL HISTORY BULLETIN. 



and other earlier observers. Tilton reported two loesses in 

 Warren county,* and in Madison county, Iowa.f The pres- 

 ent writer reported differentiation in the loess at Council 

 Bluffs. X Calvin discovered two distinct beds of loess in Page 

 county, Iowa.§ During the past summer professor Calvin 

 found two superimposed loesses i.i sec. 20, Rluffton township, 

 Winneshiek county, Iowa, the lower, evidently pre-Iowan, 

 being bluish-gray, with very large iron-tubules and numerous 

 lime-nodules, while the upper is yellow and homogeneous. 

 The writer subsequently examined a similar exposure in sec. 

 3, Decorah township, and several were observed in other parts 

 of the county. In these exposures the line separating the two 

 loesses is distinct, and they evidently differ very much in age. 

 Even more striking is the case of two loesses, both fossilifer- 

 ous, discussed by Udden in Rock Island county, Illinois, and 

 reported by L,everett,|| for they are separated by more than 

 90 feet of drift and black soil. Loess is found upon the Wis- 

 consin, the Iowan, the Illinoisan and the Kansan drift-sheets, 

 and some of it is evidently pre-Iowan. Certainly all of it is 

 not Iowan.^[ 



Southward, in the regions not reached by the later drift- 

 sheets, including therefore the vicinity of Lansing, there were 

 no such abrupt interruptions in the deposition of loess, and 

 this continued to the present time, possibly in varying degree, 

 through all the climatic changes which so materially modified 

 the northern surfaces, but southward probably affected only 

 the character of the vegetation. Thus a deposit of southerly 

 loess might be the equivalent in age of several of the north- 

 ern drift periods, without showing lines of demarkation be- 

 tween the several periods, which in the south were more or 



*Ia. Geol. Sur. , vol. v, pp. 318-19. 

 tProc. la. Acad. Sci., vol. iv, p. 49. 



+ Proc. la. Acad. Sci., vol. vi, pp. 107-8; Jour, of Geol., vol. vii, pp. 

 132-3, 1899. 



§Ia. Geol. Sur., vol. xi, pp. 444-5, 1901. 



IIU. S. Geol. Sur., vol. xxxviii, p. 115: 1899. 



IfSee paper on Loess and the Iowan Drift, which follows. 



